Respirators are frequently worn by people working in areas where the air may be contaminated with toxic or noxious substances such as particulates, gases and vapors. For example, the air in a sanding or grinding area may contain airborne particulates, the air in a painting area may contain droplets of paint or solvent vapors, and the air in a welding area may contain harmful particles or fumes. The respirator may filter the air or it may provide a supply of uncontaminated air.
A respirator may include a helmet or similar device for impact protection. Respirators that include helmets are frequently worn by people working in areas where there is a potential for impact from a foreign object. Typically, this type of respirator comprises a helmet with an air inlet, face shield, and an independent air supply.
The face shield has a lens that may be a permanent part of the face shield or it may be removable and replaceable in a frame. In many instances, a replaceable lens may be more economical to replace than having to replace the entire face shield. However, because the lens is used in a respirator function, the attachment system should provide an adequate seal. In addition, the lens as installed should provide for some level of impact protection.
Various government agencies and industry organizations define certain requirements and standards for protective gear, including helmets and respirators. For example, the National Institute of Occupational Safety and Health (NIOSH) certifies certain safety equipment, such as respirators, for the workplace and the American National Standards Institute (ANSI) recommends voluntary consensus industry standards, such as high mass and high velocity impact, in the United States. Other agencies and organizations around the world establish standards for helmets and respirators. Attempts to meet these types of standards and requirements have resulted in fairly complex attachment systems for replaceable lenses for respirators.
For example, U.S. Pat. No. 4,097,929 describes a protective visor that has an arcuately curved frame that receives a flexed sheet of resilient transparent material. The sheet is attached to the outside of the frame using mutually offset lugs. The sheet is inserted through a fairly complex process of pressing on the rear surface of the visor panel in the region of one of the outer lugs and simultaneously pressing from the front at the vertical edge of the visor panel. The lugs are on the outside frame of the face shield.